The present invention relates generally to freezers for cryogenic treatment of metals and other materials and, more particularly, to a freezer and plant gas system that harnesses the cooling properties of the plant gas evaporator in a manner that facilitates energy and cryogen savings, as well as, thermal processing automation and optimization.
Recently, substantial attention has been drawn to cryogenic treatment of metal parts and tools. The cryogenic treatment process tends to enhance a metal""s mechanical properties such as wear resistance, hardness, and dimensional stability. Manufacturing companies, which replace thousands of worn out tools every year at a tremendous cost to the company and the consumer, are turning to cryogenic treatment processes in growing numbers in an effort to increase tool life and reduce costs. Use of the cryogenic treatment process has also found its way into high performance applications and consumer type products. For instance, cryogenic treatment processes are used to enhance the performance and durability of auto racing cars, the accuracy of firearms, the performance of baseball bats and golf clubs, the tonal quality of musical instruments, and the accuracy of aeronautical measuring devices. It also plays an integral part in the construction of satellites, interplanetary probes, and ground and space based telescopes. Other areas in which the cryogenic treatment process is being used include the fields of medicine, genetics, and semiconductors.
The cryogenic treatment process typically includes the use of liquid cryogen, such as nitrogen or some other inert gas, to significantly cool parts or specimens well below zero degrees Fahrenheit (F); in some instances, all the way down to minus 320xc2x0 F. The cooling is typically accomplished in a xe2x80x9ccold boxxe2x80x9d or insulated freezer compartment supplied with a liquid cryogen from a liquid storage tank.
Most facilities with freezer installations also include plant processes, such as heat treating, that utilize inert gas. To supply gas to these processes, evaporators, which enables the liquid cryogen to expand to gas, are installed near the liquid storage tank, usually on the same pad and typically in xe2x80x9cfree airxe2x80x9d to take advantage of maximum heat exchanging properties. A drawback to placing the evaporators in xe2x80x9cfree airxe2x80x9d is that a significant amount of cooling energy is unnecessarily wasted. Harnessing this energy could prove to be advantageous to overall plant processes and economics.
Another drawback to established freezer installations is the location of the freezer. Typically, the freezer is installed in the immediate vicinity of the liquid storage tank to ensure liquid is available in a reasonable amount of time when called for in the cooling process. This location may be a significant distance from the location most beneficial to the overall process and economics of a plant. For example, in heat treatment facilities, it may be desirable to locate the freezer on the other side of the-plant within an automated thermal processing line, which would allow an operator to include heat treatment and cryogenic treatment in the treatment xe2x80x9crecipexe2x80x9d for a given part or tool. However, the farther the freezer is located away from the liquid storage tank, the less efficient the freezer system will operate.
The inefficiency of the freezer system is due to the expansion of the liquid cryogen to gas within the liquid supply conduit. Specifically, the liquid cryogen will expand into gas in the conduit in which it is transported until the conduit itself is cooled below the temperature at which the cryogen will liquefy or stay in liquid form. The farther the freezer is away from the liquid source, the more gas that will evaporate and expand in the conduit and be wasted in the freezer, until the conduit is cooled and liquid reaches the freezer. Because freezer use is intermittent in most freezer installations, the liquid cryogen will typically re-expand along the conduit as the freezer and conduit warm between cooling processes. As a result, significant quantities of gas will likely be wasted upon each use of the freezer.
One way to combat this waste is to locate the freezer in the immediate vicinity of the liquid storage tank. But as noted above, this requires locating the freezer remotely from the designed heat/cryogenic treatment process and, thus, creates excessive labor costs due to material handling and transportation to and from the balance of the process. Alternatively, a cryogenic pumping system could be used to provide constant pressure to prohibit expansion of the liquid cryogen to gas in the piping system. However, such systems tend to be very costly to purchase and install, as well as, operate and maintain.
Thus, it would be desirable to provide a freezer and plant gas system in which the freezer can be located remotely from the liquid storage tank, wherein liquid is supplied to the freezer on demand without excessive wasting of gas, and wherein the cooling energy of the plant gas evaporation process can be harnessed.
The present invention is directed to an improved freezer and plant gas system that harnesses the cooling properties of the plant gas evaporator to facilitate energy and cryogen savings, as well as the automation and optimization of a plant thermal processing system. In a particularly innovative aspect of the invention, the freezer includes an internally mounted evaporator sized to meet the gas requirements of the plant processes requiring inert gas. By evaporating the plant gas in the freezer, the freezer can be remotely located from the liquid cryogen source while making liquid cryogen available when called for during a cryogenic treatment process of metal and other materials. In addition, by evaporating in the freezer the freezer advantageously harnesses the cooling properties of the evaporator to pre-cool the freezer and material to be treated prior to any use of liquid cryogen in the cooling process; resulting in significant cryogen and energy savings.
In another innovative aspect of the invention, a liquid load basket is adapted to economically thermally treat materials in a deep cryogenic treatment process.
Other innovative aspects of the invention include the preceding aspects individually or in combination.
Other aspects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.